JP3295785B2 - Switch circuit and ultrasonic diagnostic apparatus using the same - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a switch circuit capable of improving an on / off switching speed at the time of signal switching, and a switch circuit for detecting a transmission pulse applied from a transmission pulse generator by using this switch circuit. The present invention relates to an ultrasonic diagnostic apparatus used as a changeover switch for switching between a received signal output from a slave and a received signal.

[0002]

2. Description of the Related Art A conventional ultrasonic diagnostic apparatus of this kind is disclosed in Japanese Patent Application Laid-Open No. 2-136134, and as shown in FIG. 4, for example, a plurality of transducer elements 11 ₁ and 1 formed in a strip shape. ₂ ,…,
A probe 2 is arranged adjacent to the sound absorbing material to transmit and receive ultrasonic waves, and each transducer element 11 1 to ₁ n in the probe 2
N-number of transmission pulse generator 3 _1, for applying a driving pulse of the launch ultrasonic giving a predetermined delay time to 3 _2, ..., 3n
And a vertical double diffusion field effect transistor (hereinafter referred to as “VD
High-voltage analog switch 4 ₁ comprising the abbreviated as MOS FET ") in reverse series, 4 _2, ..., transmitting the oscillator element 1 ₁ 1n of the probe 2 with 4n pulse generator 3 ₁ ~
And a changeover switch 5 for switching the connection with 3n.

[0003] Here, the high-voltage analog switch 4 ₁ to 4n used as the changeover switch 5 is configured as shown in the internal circuit diagram of a first high-voltage analog switch shown by reference numeral 4 ₁ I have. That is, two VDs
A gate driver 11 having an optical coupling circuit composed of MOS FETs 8a and 8b, a light emitting diode 9 and a photovoltaic diode array 10 and generating a photovoltaic current in response to a control signal from an input terminal; a diode 12 and an enhancement mode The above V
The control unit 14 operates at the time of restoration of the DMOS FETs 8a and 8b and short-circuits between the gate and the source to expedite restoration.

[0004] the high-voltage analog switch of the above-mentioned 4 ₁ ~4n
Is such that the potential between the gate and the drain of the two VD MOS FETs 8a and 8b is supplied by an optical coupling circuit composed of the light emitting diode 9 of the gate driver 11 and the photovoltaic diode array 10. Where VD
Since the MOS FETs 8a and 8b have parasitic diodes 15a and 15b, respectively, two of them are connected in anti-series as shown in the figure to be used as an AC switch. By using the switch circuit having such a configuration, when a control signal is applied to the input terminal, the light emitting diode 9 emits light, and this light enters the photovoltaic diode array 10 to generate a photovoltaic current. And VD MOS FETs 8a and 8b
Charge the gate capacity of Then, the gate voltage is increased by this charging, and the VD MOS FETs 8a and 8b are turned on. Next, when the control signal is removed from the input terminal, the light emission from the light emitting diode 9 stops, and the control unit 14 switches to operate the VD MOS FETs 8a, 8a.
By short-circuiting between the gate and the source of b, the charge of the gate is discharged to turn off the VD MOS FETs 8a and 8b.

[0005] Next, the high-voltage analog switch 4 ₁
A description will now be given of a conventional method used to shorten the time for turning on and off the VD MOS FETs 8a and 8b in .about.4n. First, in FIG. 5 and a drive circuit which can be closed by the first high-voltage analog switch 4 _first internal circuit and a high speed it shown in FIG. Next, in FIG. 5, an example of the relationship between the forward current If of the light emitting diode 9 of the gate driver 11 and the open circuit voltage Voc is shown in FIG. Here, the parameter Rsh indicates the size of the shunt resistor 16 at the output terminal of the gate driver 11. Now
Since the voltage between the source and the gate of the VD MOS FETs 8a and 8b is equivalent to a capacitor, the voltage eg between the source and the gate is obtained.
Is increased to a potential at which the VD MOS FETs 8a and 8b are turned on at a high speed by increasing the shunt resistance 16 of the gate driver 11 and increasing the forward current If of the light emitting diode 9.
Since the gate of 8b is charged at high speed, it is clear that the on-speed is improved. However, when the shunt resistor 16 is increased, the VD MOSF
Since the speed at which the ETs 8a and 8b are turned off decreases, increasing this value is limited.

On the other hand, to increase the on-rate by increasing the forward current If of the light emitting diodes 9 of the gate driver 11, the VD MOS FET 8a, if to be turned on in conjunction with 8b, this high-voltage analog switch 4 ₁ It is difficult to increase the overall power consumption and to be restricted from the maximum rating of the forward current of the light emitting diode 9. Therefore, in order to drive the gate driver 11, when a rectangular wave voltage E is applied as shown in FIG.
A large current flows instantaneously only immediately after this voltage is applied to the light emitting diode 9. After the gates of the VD MOS FETs 8a and 8b are set to a specified value, if they are kept at a steady value, the ON time can be reduced. This is effective for reducing power consumption.

Here, as shown in FIG. 5, a voltage E is applied to the light emitting diode 9 via a circuit comprising resistors 17, 18 and a capacitor 19. Now, the above resistor 1
7, 18 and the value of the capacitor 19 are R, R ',
C. When a rectangular wave voltage of voltage E is applied to the input terminal of the gate driver 11, the light emitting diode 9
, A large current flows at the moment E / R, and the time constant determined by C and R After a much longer time, a steady current of E / (R + R ') will flow. Therefore, the above gate driver 1
In response to the magnitude of the forward current If of the light-emitting diode 9, a voltage given from the relation shown in FIG. 6 is generated at its output terminal.
The gates of the MOS FETs 8a and 8b are charged.

The forward current If of the light emitting diode 9 at this time is
FIG. 7 shows the state of the source-gate voltage eg of the VD MOS FETs 8a and 8b. Now
At the moment when the rectangular wave voltage E is applied to the gate driver 11 as shown in FIG.
A large current of R flows through the light emitting diode 9, and the source-gate voltage eg rapidly rises as shown in FIG. However, as shown in FIG. 7B, since the current rapidly decreases within the time constant of the light emitting diode 9, VD
Before the source-gate voltage eg reaches the value before the MOS FETs 8a and 8b are turned on, the rate of increase of the voltage decreases.

When the current of the light emitting diode 9 is stopped, the gate voltage of the VD MOS FETs 8a and 8b is determined by the time required for discharging the electric charge charged in the capacitance between the source and the gate. At this time, VDM for controlling a large current
Since the capacitance between the source and the gate of each of the OS FETs 8a and 8b is large, the control unit 14 including the enhancement mode p-channel FET 13 and the diode 12 in which the capacitance between the source and the gate is small has the above-mentioned VDM.
The electric charges stored in the gates of the OS FETs 8a and 8b are rapidly discharged, the gate voltage is reduced, and the VD
The MOS FETs 8a and 8b are turned off. That is, when the output voltage of the photovoltaic diode array 10 becomes zero, the diode 12 of the control unit 14 becomes non-conductive, and the p-channel FET 13 becomes the VD MOS FET 8a,
8b operates to short-circuit the source and the gate. Even if the capacitance between the source and the gate of the VD MOS FETs 8a and 8b is large, if the on-resistance of the p-channel FET 13 is sufficiently small, it corresponds to a voltage change determined by the capacitance between the shunt resistor 16 and the two terminals. VD at the speed of
The MOS FETs 8a and 8b are turned off.

[0010]

Turning on the conventional high voltage analog switches 4 ₁ to 4n shown in FIG. 4 [0008] rate, 5
Is determined by the circuit composed of the resistors 17 and 18 and the capacitor 19 shown in FIG. Here, if the value R of the resistor 17 is reduced, the on-speed is improved, but the peak value of the forward current If of the light emitting diode 9 is increased. Therefore, it is difficult to reduce the value R of the resistor 17 because it has an adverse effect on power supply voltage fluctuations and the like. That is, in the circuit shown in FIG. 5, there is a limit in improving the ON speed. On the other hand, the off-rate of the high-voltage analog switch 4 ₁ to 4n are corresponding to the time constant determined by the electrostatic capacitance between the shunt resistor 16 at both terminals (including the capacitance between the source and the gate of the p-channel FET 13) Speed. Here, when the resistance value of the shunt resistor 16 is reduced, the off-speed is improved. However, as is clear from the characteristic diagram of the gate driver 11 shown in FIG. 6, the terminal voltage of the photovoltaic diode array 10 decreases, As a result, the ON speed is reduced. For these reasons, conventional high voltage analog switches 4 ₁
In 4n, there is a limit in improving the on / off speed, and it is difficult to further increase both.

In view of the above, the present invention addresses such a problem, and a switch circuit capable of improving the on / off switching speed at the time of signal switching, and applying the switch circuit from a transmission pulse generator to the switch circuit. It is an object of the present invention to provide an ultrasonic diagnostic apparatus which is used as a changeover switch for switching between a transmission pulse to be transmitted and a reception signal output from a probe.

[0012]

In order to achieve the above object, a switch circuit according to the present invention uses two field effect transistors connected in reverse series as a switching element, and uses the source / gate of the two field effect transistors. A high voltage analog switch for controlling the voltage between the optical circuit and switching the connection of the target circuit, and a switch control circuit having the same circuit configuration as the high voltage analog switch and the high voltage analog switch An amplifier for detecting a voltage between the source and the gate of the two field effect transistors in the switch control circuit and amplifying a difference voltage between the detected voltage and an on / off reference voltage. A negative feedback circuit for applying a signal voltage to an optical coupling circuit in the switch control circuit is provided.

A photocoupler is connected between the source and the gate of the two field-effect transistors in the high-voltage analog switch and the switch control circuit, and the source / gate of the field-effect transistor is supplied by an external signal input to the photocoupler. A short circuit may be provided.

Further, an ultrasonic diagnostic apparatus as a related invention of the above-mentioned switch circuit has a probe in which a plurality of transducer elements are arranged and which transmits and receives ultrasonic waves, and a transducer provided in each of the transducer elements in the probe. A transmission pulse generator for applying a drive pulse for ultrasonic launch by giving a delay time of, a transmission pulse applied to the probe from the transmission pulse generator, and a reception signal from the probe Switch, a receiving amplifier that amplifies a signal received from the probe output through the switch, and a delay circuit that applies a predetermined delay time to the signal received from the receiving amplifier. A delay circuit that adds and outputs the received signals whose phases have been aligned by these delay circuits, a detector that detects the signal that has been phased by the delay circuit, and an output signal from the detector. Display device for displaying as an image That the ultrasonic diagnostic apparatus, as the changeover switch, but using a switch circuit of the unit.

[0015]

The switch circuit configured as described above switches the connection of the target circuit by a high-voltage analog switch, and has the same circuit configuration as the high-voltage analog switch provided in parallel with the high-voltage analog switch. A switch control circuit, and a negative feedback circuit provided at an input portion of the switch control circuit detects a voltage between the source and the gate of the two field effect transistors in the switch control circuit and detects the detected voltage. It operates so as to amplify the difference voltage between the ON / OFF reference voltage and the amplified signal voltage and apply the amplified signal voltage to the optical coupling circuit in the switch control circuit. This makes it possible to improve the on / off switching speed at the time of signal switching.

Further, the ultrasonic diagnostic apparatus configured as described above is provided as a changeover switch for switching between a transmission pulse applied from a transmission pulse generator to a probe and a reception signal from the probe. By using the above-described switch circuit, the switching speed of on / off at the time of signal switching can be improved, and the ultrasonic scanning speed can be improved.

[0017]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Embodiments of the present invention will be described below in detail with reference to the accompanying drawings. FIG. 1 is a circuit diagram showing an embodiment of a switch circuit according to the present invention. The switch circuit Similarly, for example reception from transmission pulse and該探probe 2 applied from the transmission pulse generator 3 ₁ 3n to probe 2 in the ultrasonic diagnostic apparatus to that shown in FIG. 4 It intended to be used as change-over switch 5 for switching a signal, reference numeral 4 ₁ 'in FIG. 1
As shown in the internal circuit diagram of the first high withstand voltage analog switch shown with, two VD MOS FETs 8a and 8
b, light emitting diode 9 and photovoltaic diode array 1
0, an optical coupling circuit, a shunt resistor 16, and a photocoupler in which the light emitting diode 22 and the phototransistor 23 are optically coupled.

In FIG. 1, a high voltage analog switch 4
Reference numerals ₁ 'to 4n' are used to select an internal transducer element when transmitting / receiving an ultrasonic wave from a probe (not shown) and connect it to a transmission pulse generator. This high voltage analog switch 4
₁ 'to 4n' are or prevent high pressure at the time of transmission, or passed through a large current at the time of reception and performs an operation to capture select signals small voltage, the terminal T _1, which is provided for each T ₂ is provided with a bidirectional characteristic of inputting and outputting a transmission / reception signal. Each unit of the high breakdown voltage analog switches 4 ₁ ′ to 4 n ′ uses two VD MOS FETs 8 a and 8 b to which source electrodes are commonly connected as switching elements. The diode 1
Reference numerals 5a and 15b denote parasitic diodes of the VD MOSFETs 8a and 8b, which operate as half-cycle rectifiers even when one VD MOSFET 8a or 8b is off. Also, two VD MOS FETs 8a, 8b
Have their source electrodes connected in common, and when they are off, both positive and negative signals are blocked.

When a forward current If flows through the light emitting diode 9 of the optical coupling circuit, the light emitting diode 9 emits light,
This light is incident on the photovoltaic diode array 10, and as a result, a photovoltaic current is generated, and the VD MOS FETs 8a and 8b
Is charged, and when a predetermined potential is reached, the VD
The MOS FETs 8a and 8b are turned on. At this time, when the voltage generated in the photovoltaic diode array 10 when a constant forward current If is applied to the light emitting diode 9 reaches a constant value, the time T during which the VD MOS FETs 8a and 8b are turned on.
and the time Toff when the voltage generated in the photovoltaic diode array 10 reaches another constant value smaller than the above when the forward current If is set to zero and the VD MOS FETs 8a and 8b are turned off. Looking at the relationship depending on the load resistance and the load resistance (shunt resistance 16), the characteristic is that Ton and Toff increase as the load capacitance increases, and that Ton decreases and Toff increases as the shunt resistance 16 increases. is there. This means that the VD MOS FET 8
When a and 8b are determined and the capacitance between the source and the gate is given, the value of the shunt resistor 16 corresponding to the load resistance is increased, and the gate capacitance is charged as quickly as possible to charge the gate to a predetermined value. This indicates that the voltage can be turned on at a high speed.

For this purpose, in the embodiment shown in FIG. 1, the switch control circuit 21 having the same circuit configuration as the above-mentioned high voltage analog switches 4 ₁ ′ to 4 n ′ is provided with the high voltage analog switches 4 ₁ ′ to 4 n ′. They are provided in parallel. further,
The input of the switch control circuit 21 detects the voltage eg between the source and the gate of the two VD MOS FETs 8a and 8b in the switch control circuit 21 and outputs the detected voltage and the on / off reference voltage Er. An amplifier 24 for amplifying the difference voltage is provided, and a negative feedback circuit for applying the amplified signal voltage to the optical coupling circuits (9, 10) in the switch control circuit 21 is provided. The output voltage of the amplifier 24 is applied to the light emitting diode 9 of the optical coupling circuit via the resistor 25. The capacitor 26 provided in parallel with the resistor 25 is for adjusting the phase of the negative feedback circuit while preventing oscillation.

If the gain of the amplifier 24 is sufficiently large, the VD MOS FET 8 in the switch control circuit 21
Until the source-gate voltage eg of a, 8b reaches the reference voltage Er, the light emitting diode 9 receives the current If = Eo / R given by the maximum output voltage Eo of the amplifier 24 and the resistance value R of the shunt resistor 16. Flows. In this case, the VD MOS FETs 8a and 8b in the switch control circuit 21
VDM in the high withstand voltage analog switches 4 ₁ ′ to 4 n ′
Since the same OS FETs 8a and 8b are used,
Its source-gate voltage eg also VD MOS FET 8a of the high-voltage analog switch 4 within _{1 '~4n',} 8b
Rises to the reference voltage Er at the same speed as. FIG. 2 shows how the source-gate voltage eg increases. VD MOS FET 8a of the high voltage analog switches 4 in the _first prior art shown in FIG. 5, the source-gate voltage eg of 8b, as shown in FIG. 2 (b), to reach a steady-state value by the C and R It is restricted by the determined time constant T and gradually rises. However, according to the present invention shown in FIG. 1, by using the amplifier 24 having a fast response speed, there is almost no restriction by the time constant T.
As shown in (a), the source-gate voltage eg of the VD MOS FETs 8a and 8b rises at a high speed.

Also, in FIG.
A voltage is applied to the light emitting diode 22 via a resistor 27 using a photocoupler in which the phototransistor and the phototransistor 23 are optically coupled.
3, by short-circuiting between the source and gate of the VD MOS FETs 8a and 8b,
The VD MOS FETs 8a and 8b can be turned off at a high speed by rapidly discharging the electric charge accumulated in the gate of b. FIG. 1 shows an example in which the light emitting diode 22 and the phototransistor 23 are combined as a photocoupler.
A light receiving element in which a junction photodiode and an amplifying transistor are integrated in one chip may be used. The same effect can be obtained by using a capacitor equivalent to the capacitance between the source and the gate of the VD MOS FETs 8a and 8b in the switch control circuit 21.

FIG. 3 is a block diagram showing an embodiment of an ultrasonic diagnostic apparatus as a related invention of the switch circuit shown in FIG. This ultrasonic diagnostic apparatus obtains a tomographic image of a diagnostic part of a subject using ultrasonic waves, and is, for example, an electronic linear scanning type, and includes a plurality of transducer elements 11 to ₁ formed in a strip shape. Probe 2 in which 1n is arranged and transmits and receives ultrasonic waves
If a transmission pulse generator 3 for applying a driving pulse of ultrasound launched giving a predetermined delay time to each oscillator element 1 ₁ 1n in the probe 2, from the transmission pulse generator 3 A changeover switch 5 for switching between a transmission pulse applied to the probe 2 and a reception signal from the probe 2, and a reception signal from the probe 2 output through the changeover switch 5 Amplifiers 6a to 6a that amplify the signal by changing the gain with time
6e and a plurality of delay circuits 7a to 7e for giving a predetermined delay time to the output signals from the respective reception amplifiers 6a to 6e. The received signals whose phases are aligned by these delay circuits 7a to 7e are added. A phasing circuit 29 having an adder 28, and a detector 30 for detecting a signal phased by the phasing circuit 29.
And a display device 31 for displaying an output signal from the detector 30 as an image.

In FIG. 3, the changeover switch 5 is configured to sequentially select, for example, five transducer element groups from one end and connect them to the next-stage reception amplifiers 6a to 6e. The five transducer element groups are sequentially switched and translated. Therefore, five receiving amplifiers (6a to 6e) are provided. Further, the operation of each of the above components is controlled by a control signal from the control unit 32.

Here, in the present invention, the changeover switch 5 has the circuit configuration shown in FIG. 1 and is a high withstand voltage analog switch 4 ₁ ′ which can improve the on / off switching speed at the time of signal switching. To 4n 'are used. With such a configuration, the ultrasonic diagnostic apparatus of the present invention, by using a switching circuit (4 ₁ '~4n') shown in FIG. 1 as the changeover switch 5, the signal switching speed of the switching on and off And the ultrasonic scanning speed can be improved.

[0026]

The switch circuit according to the present invention (see FIG. 1)
Is configured as described above, the connection of the target circuit is switched by the high voltage analog switch, and the switch control is provided in parallel with the high voltage analog switch and has the same circuit configuration as the high voltage analog switch. A negative feedback circuit provided at the input of the switch control circuit, detects the voltage between the source and gate of the two field-effect transistors in the switch control circuit, and switches the detected voltage on and off. , And the amplified signal voltage can be applied to the optical coupling circuit in the switch control circuit. This makes it possible to improve the on / off switching speed at the time of signal switching.

The ultrasonic diagnostic apparatus according to the present invention (FIG. 3)
) Is configured as described above, so that the above-described switch circuit is used as a changeover switch that switches between a transmission pulse applied from the transmission pulse generator to the probe and a reception signal from the probe. By using this, it is possible to improve the ultrasonic scanning speed by improving the on / off switching speed at the time of signal switching.

[Brief description of the drawings]

FIG. 1 is a circuit diagram showing an embodiment of a switch circuit according to the present invention.

FIG. 2 is a graph showing transient characteristics of a voltage of a high voltage analog switch in the switch circuit.

FIG. 3 is a block diagram showing an embodiment of an ultrasonic diagnostic apparatus as a related invention of the switch circuit shown in FIG. 1;

FIG. 4 is a circuit diagram showing a changeover switch in a conventional ultrasonic diagnostic apparatus.

FIG. 5 is a circuit diagram showing an internal configuration of a high voltage analog switch as the changeover switch.

FIG. 6 is a graph showing input / output characteristics of a gate driver in the high breakdown voltage analog switch.

FIG. 7 shows the transient characteristics of the input voltage (a) of the gate driver, the forward current (b) of the light emitting diode, and the source-gate voltage (c) of the VD MOS FET in the high voltage analog switch shown in FIG. It is a graph shown.

[Explanation of symbols]

1 ₁ 1n ... vibrator element 2 ... probe 3,3 ₁ 3n ... transmission pulse generator 4 ₁ 'to 4n' ... high-voltage analog switch 5 ... changeover switch 6a to 6n ... receiving amplifier 8a, 8b ... VD MOS FETs 9 and 22 Light-emitting diode 10 Photovoltaic diode array 21 Switch control circuit 23 Phototransistor 24 Amplifier 29 Phase-adjusting circuit 30 Detector 31 Display device 32 Control unit

──────────────────────────────────────────────────続 き Continuation of the front page (56) References JP-A-51-15368 (JP, A) JP-A-62-240032 (JP, A) JP-A-2-136134 (JP, A) JP-A-4- 301919 (JP, A) (58) Field surveyed (Int. Cl. ⁷ , DB name) A61B 8/00

Claims (3)

(57) [Claims] 1. A two-field effect transistor is connected in anti-series and used as a switching element, and a voltage between a source and a gate of the two field-effect transistors is controlled by an optical coupling circuit to switch connection of a target circuit. A switch control circuit having a high withstand voltage analog switch and having the same circuit configuration as the high withstand voltage analog switch is provided in parallel with the high withstand voltage analog switch, and the source and gate of two field effect transistors in the switch control circuit are provided. A negative feedback circuit for detecting an intermediate voltage and amplifying a difference voltage between the detected voltage and an on / off reference voltage, and applying the amplified signal voltage to an optical coupling circuit in the switch control circuit. A switch circuit characterized by being provided. 2. The high-voltage analog switch and the source of two field effect transistors in the switch control circuit.
2. The switch circuit according to claim 1, wherein a photocoupler is connected between the gates, and a source-gate of the field effect transistor can be short-circuited by an external signal input to the photocoupler. 3. A probe in which a plurality of transducer elements are arranged to transmit and receive ultrasonic waves, and a drive pulse for ultrasonic emission is applied by giving a predetermined delay time to each transducer element in the probe. A transmission pulse generator, a switch for switching between a transmission pulse applied from the transmission pulse generator to the probe and a reception signal from the probe, and an output through the switch. Receiving amplifier for amplifying the received signal from the probe to be received, and a received signal having a delay circuit for giving a predetermined delay time to the received signal from the received amplifier, the phases of which are aligned by these delay circuits A phasing circuit that adds and outputs
2. The ultrasonic diagnostic apparatus according to claim 1, further comprising: a detector for detecting the signal phase-adjusted by the phase adjusting circuit; and a display device for displaying an output signal from the detector as an image. Or an ultrasonic diagnostic apparatus using the switch circuit according to 2.